[4 + 2]-Cycloaddition of maleic anhydride to substituted cycloheptatrienes for the synthesis of novel 4-oxatetracyclo[5.3.2.02,6.08,10]dodec-11-ene-3,5-diones

The [4+2]-cycloaddition of maleic anhydride to 7-substituted 1,3,5-cycloheptatrienes involves their 7-R-bicyclo[4.1.0]-hepta-2,4-diene tautomers and affords new 4-oxatetra- cyclo[5.3.2.0^2,6.0^8,10]dodec-11-ene-3,5-diones in 85–95% yields. The structure of the resulting adducts is proved using advanced 1D and 2D NMR techniques and X-ray diffraction analysis. The cycloaddition proceeds stereo specifically providing meso-(1S*,2S*,6R*,7R*,8R*,9-anti,10S*)-configuration in the products